Thermal preparation of alkylamides

ABSTRACT

A method of preparing alkylamides which comprises contacting an alpha-nitroketone with a polar aprotic solvent at a temperature of about 70* to 200*C. The alkylamides herein prepared are useful as fuel and lubricant additives and as intermediates in the preparation of acids, nitriles and amines.

United States Patent Duranleau et al. Dec. 9, 1975 [5 THERMALPREPARATION OF 3,562,302 2/1971 Ellis 6. 260/561 R ALKYLAMIDES 3,772,35811/1973 Lang 260/404 3,776,901 12/1973 Kelly et al 260/561 R lnventorsrRoger Duranleau, Ardonia; J 3,862,185 1/1975 Love 6161. 2 260/561 R F.Matteo, Wappingers Falls, both of NY Assignee: Texaco Inc., New York,NY.

Filed: Dec. 12, 1974 Appl. No: 532,423

US. Cl. 260/404; 260/561 R lnt. Cl. C07C 103/02 Field of Search .1260/404, 56l R References Cited UNITED STATES PATENTS l2/l970 Ellis260/404 Primary Examiner-C. Davis Attorney, Agent, or Firm -Th0mas H.Whaley; Carl G,

Ries; George J. Darsa ABSTRACT 16 Claims, No Drawings THERMALPREPARATION OF ALKYLAMIDES BACKGROUND OF THE INVENTION This inventionrelates to a novel method of preparing alkylamides fromalpha-nitroketones. In particular, it relates to a thermal non-catalyticmethod for preparing alkylamides from terminal alpha-nitroketones.

Alkylamides have previously been prepared by the amination of carboxylicacids. Many carboxylic acids, however, are not easily available incommerce and particularly those acids containing an odd numbered carbonchain. To prepare the acids, moreover, requires costly processing as byoxidizing the corresponding alcohol or by Grignard synthesis. Anothermethod of preparing alkylamides is by converting nitro-nitrosoalkanedimers by reaction with at least molar amounts of an anhydrous mineralacid over relatively short contact times. However, this method is notcommercially attractive inasmuch as the mineral acid is consumed duringthe reaction and low concentrations of the acid reactant must beemployed so as to avoid explosive conditions.

A novel method has now been discovered whereby alkylamides having from 2to SI carbons can be provided in good yields.

SUMMARY OF THE INVENTION Broadly, this invention contemplates a methodof preparing an alkylamide which comprises contacting analpha-nitroketone with an oxygenated polar aprotic solvent at atemperature of about 70 to 200C. The transformation produces carbondioxide as a by-product.

According to our invention the alpha-nitroketone thermally converted tothe alkylamide is a terminal vicinal nitroketone and corresponds to theformula:

where R is an alkyl group having I to 50 carbon atoms. It is essentialto the method of this invention that tenninal alpha-nitroketones, i.e.,l-nitro-2-alkanones, be employed. Non-terminal alpha-nitroketones, thatis nitroketones where the nitro group is on other than a terminalcarbon, do not undergo thermal conversion to alkylamides as herein morefully described.

The method of the invention is further explained by the followingequation:

where R is as heretofore defined and where a by-product of the method iscarbon dioxide. It will be observed that the alkylamide possesses onecarbon less than the starting nitroketone such that the conversionreaction involves transformation of the nitroketone throughrearrangement and cleavage.

According to this invention the contemplated alkylamides are derivedfrom alpha-nitroketones corresponding to the formula above and includeas starting materials l-nitro-Z-propanone, l-nitro-2-butanone,l-nitro-2- pentanone, l-nitro-2-hexanone, l-nitro-2-heptanone,l-nitro-2-octanone, l-nitro-Z-decanone, l-nitro-Z- dodecanone,l-nitro-2-pentadecanone, l-nitro-2-hexadecanone,I-nitro-Z-heptadecanone, and l-nitro-2- eicosanone. Mixtures of thealpha-nitroketones can be converted to the corresponding mixture ofamides. The nitroketones contemplated as starting materials and listedabove can be prepared in accordance with the procedures described in theart as, for example, in US. Pat. No. 3,557,166.

In one embodiment, the method of this invention comprises heating thenitroketone as hereinabove described at a temperature of about to 200C.in the presence of an oxygenated polar aprotic solvent. The class ofsolvents employed in the instant method is a key factor in the reaction.l-lydrolytic solvents, that is polar protic solvents, such as alcoholsor water produce products other than alkylamides such as esters or acidsand nitroalkanes. No reaction occurs under the operating conditionsdescribed herein when non-polar solvents, such as benzene, hexane andtoluene or nonoxygenated polar aprotic solvents such as methylenechloride, chloroform and l,2-dichlorobenzene are employed.

The comtemplated oxygenated polar aprotic solvents employed herein areillustrated by alkylformamides, alkylacetamides, alkylsulfoxides,alkylureas, alkylphosphoramides, alkylpyrrolidinones, aldehydes, ketonesand ethers.

Specific examples of the solvents employed in the instant method aredimethylformamide, diethylformamide, dimethylacetamide,dimethylsulfoxide, diethylsulfoxide, tetramethylurea, tetraethylu rea,hexamethylphosphoramide, l-methyl-2-pyrrolidinone, l-ethyl-2-pyrrolidinone, l,4-dimethyl-2-pyrrolidinone, butyraldehyde, acetone,methylethylketone, diethylether, 1,4- dioxane, tetrahydrofuran andtetrahydropyran. Mixtures of oxygenated polar aprotic solvents can alsobe used. A highly preferred oxygenated polar aprotic solvent isdimethylsulfoxide. In general, any oxygenated aprotic solvent that is aliquid under the processing conditions set forth herein can be employed.

The mole ratio of nitroketone oxygenated polar aprotic solvent employedin the instant method is an important factor insofar as providingsubstantial yields of alkylamide. Suitably, the mole ratio ofnitroketone to oxygenated polar aprotic solvent employed herein rangesfrom about 1:3 to 1:100, preferably from 1:10 to 1:50. An inert liquiddiluent can be employed, if desired, to promote the contact of thenitroketone and oxygenated polar aprotic solvent. A suitable inertliquid diluent is one having a boiling point between about and 200C,such as heptane, chlorobenzene, ethylbenzene, cumene, cymene and durene.

The reaction temperature employed in the method wherein terminalalpha-nitroketones are converted to alkylamides is generally from aminimum of at least 70C. up to 200C, preferably from about to C.Further, the method can be undertaken at pressures of from atmosphericup to 300 p.s.i.g. The reaction time is usually about 1 and 24 hoursalthough longer or shorter periods may be employed depending upon theoxygenated polar aprotic solvent used and the temperature conditionsemployed. Further, the reaction described herein should be undertaken ina substantially anhydrous medium wherein less than about 3 weightpercent water is introduced to the reaction. Water if introduced inamounts greater than about 3 peight percent substantially diminishes theyield of am- I e.

Specific examples of the alkylamides prepared by the instant methodinclude acetamide, propanamide, butanamide, 3-methylbutanamide,pentanamide, hexanamide, octanamide. dodecanamide, pentadecanamide andnonadecanamide.

In another embodiment of the invention a method is comtemplated whereinl-olefins of from 3 to 52 carbons are converted to alkylamides. Morespecifically, the method involves first contacting a l-olefin of theformula RCH=CH where R is as heretofore defined. with a mixture ofdinitrogen tetroxide and oxygen at a temperature between about 40 and20C. employing reactant mole ratios of olefin to dinitrogen tetroxide tooxygen between about l:0.5:l and l:l.5:30. where the moles of oxygen isat least equivalent and preferably in excess to the moles of dinitrogentetroxide used. After a reaction time normally between about A and Ihours. a nitroalkylperoxy nitrate ofthe formula:

IONO, R-- H-CH,

is formed where R is as previously described. The nitroalkylperoxynitrate is thereafter contacted in a second stage with a denitratingagent of the group recited in US. Pat. No. 3,557,l66 which is hereinincorporated by reference. Illustrative of the denitrating agents aredimethylformamide, diethylformamide, dimethylacetamide,dimethylsulfoxide, diethylsulfoxide, tetramethylurea and tetraethylurea.Other denitrating agents include alkylpyrrolidinones such asl-methyl-Z-pyrrolidinone, l-ethyl-2-pyrrolidinone and 1,4-dimethyl-2-pyrrolidinone. A highly preferred denitrating agent in the presentinvention is dimethylsulfoxide. The second stage is undertaken employingmole ratios of denitrating agent to peroxy compond of at least 1:1 toabout :l at temperatures of between about 60 and 70C. to form anitroketone of the formula hereinbefore described. In the third stage,the nitroketone is contacted in an oxygenated polar aprotic solvent, ahighly preferred solvent being dimethylsulfoxide, under the conditionsprescribed above thereby thermally converting the nitroketone to analkylamide.

At the completion of the reaction, the alkylamide formed in theconversion reaction is recovered by cooling the reaction mixture andisolating the resulting solid or by chilling the reaction mixture withwater and recovering the crystals so formed. Contacting with water isundertaken at temperatures below 60C. to avoid hydrolysis of the amideand is best conducted with iced water. Any unconverted nitroketone alongwith the oxygenated polar aprotic solvent and diluent, if employed, areseparated for use in a subsequent or continuous reaction. Theco-product, carbon dioxide, can be recovered, if desired, in the courseof the reaction or at the completion thereof by scrubbing the exit gaswith an amine base at room temperature. The carbon dioxide canthereafter be recovered by thermally decomposing the aminecarbon dioxidecomplex. The oxygenated polar aprotic solvent is not consumed in themethod and can be suitably reused.

The alkylamide products of this invention are useful as fuel additives,solvents for waxes, dye solubilizers, fuel and lubricant additives, foamstabilizers in synthetic detergents, plasticizers for polymers and asreaction diluents. Further, they are useful as intermediates in thepreparation of fabric water repellents and the alkylamides preparedaccording to the inventive method may be hydrolyzed, dehydrated orhydrogenated to form their corresponding acids, nitriles and aminesuseful in soaps, cosmetics and fabric softeners.

In order to more fully illustrate the nature of our invention and themanner of practicing the same, the following examples are presented.

EXAMPLE I A 100 milliliter solution composed of 12.0 grams (0.042 mole)of l-nitro-Z-hexadecanone in dimethylsulfoxide (1.12 mole) was heated to[30C. An exotherm occurred accompanied by an evolution of gas causingthe temperature to rise to 158C. The solution was thereafter maintainedat about l50C. for a total of 2 hours. 25 milliliter samples wereremoved every onehalf hour and poured into 25 milliliters of ice water.The resulting mixture was filtered and the solids were dried at 100 mm.Hg. and 25C. Analysis by infrared and nuclear magnetic resonance of thesamples indicated that the product was predominantly pentadecanamidealong with some unreacted nitroketone. 2.67 grams of amide wererecovered corresponding to a yield of percent.

EXAMPLE ll A solution of 24.0 grams (0.084 mole) of l-nitro-2-hexadecanone in 90 milliliters of dimethylsulfoxide l. 12 mole) washeated to l00C. and the accompanying exotherm raised the temperature to170C. The temperature was thereafter maintained for 2 hours at aboutl48C. whereupon the product was poured into milliliters of ice water andfiltered. The solids (29.43 grams) were air dried and analyzed byinfrared and nuclear magnetic resonance. The analyses showed the productto be mainly pentadecanamide along with about 5 to lO percentpentadecanoic acid.

EXAMPLE Ill The procedure of Example I was followed except that l.l7mole of dimethylformamide was substituted for dimethylsulfoxide as thesolvent and sampling occurred once every hour. Analyses showed thatafter 3 hours the nitroketone was converted to the alkylamide.

EXAMPLE IV A 100 milliliter solution of 12.0 grams (0.042 mole) ofl-nitro-2-hexadecanone and 6.6 grams (0.084 mole) of dimethylsulfoxidein l,2-dichlorobenzene was maintained at l50C. for 6 hours. Samples wereperiodically removed and analyzed by infrared which showed that after 6hours no measurable conversion of the nitroketone to the amide hadoccurred. The procedure was repeated except using 3.3 grams (0.042 mole)of dimethylsulfoxide which gave identical results. This exampleillustrates that mole ratios of nitroketone to oxygenated polar aproticsolvent of less than 1:3 are inoperative in the inventive method.

EXAMPLE V The procedure of Example I was repeated except that thereaction was maintained under an atmosphere of argon and the gasescollected. Infrared analysis and mass spectrographic analysis revealedthe collected gas to be composed of 83.7% carbon dioxide, 9.0% argon,2.7% carbon monoxide and 1.7% methyl sulfide.

We claim:

1. A method of preparing an alkylamide which comprises contacting analpha-nitroketone with an oxygenated polar aprotic solvent at atemperature of from about 70C. to 200C.

2. A method according to claim 1 wherein said temperature is from about90 to 170C.

3. A method according to claim 1 wherein the mole ratio of saidnitroketone to said solvent is from about 1:3 to lzlOO.

4. A method according to claim 1 wherein the mole ratio of saidnitroketone to said solvent is from about 1:10 to l:50.

5. A method according to claim 1 wherein said contacting is at apressure of from atmospheric to 300 p.s.1.g.

6. A method according to claim 1 wherein said solvent isdimethylsulfoxide.

7. A method according to claim 1 wherein said solvent isdimethylformamide.

8. A method according to claim 1 wherein said solvent isl-methyl-2-pyrrolidinone.

9. A method according to claim 1 wherein said solvent is acetone.

]0. A method according to claim 1 wherein said solvent isdimethylacetamide.

6 11. A method according to claim I wherein said contacting is conductedin the presence of an inert liquid diluent boiling between about 80 and200C 12. A method according to claim 1 wherein said alpha-nitroketonecorresponds to the formula:

where R is an alkyl group having l to 50 carbon atoms.

13. A method according to claim 1 wherein said nitroketone isl-nitro-2-propanone and where said alkylamide is acetamide.

14. A method according to claim 1 wherein said nitroketone isl-nitro-2-hexadecanone and where said alkylamide is pentadecanamide.

15. A method according to claim 1 where carbon dioxide formed as aco-product is recovered.

16. A method of preparing an alkylamide which comprises (I)nitrooxidizing a l-olefin by contacting with dinitrogen tetroxide andoxygen to form a nitroalkylperoxy nitrate, (2) contacting said peroxynitrate with a denitrating agent to form an alpha-nitroketone and (3)contacting said nitroketone with an oxygenated polar aprotic solvent ata temperature of from about C. to 200C.

1. A METHOD OF PREPARING AN ALKYLAMIDE WHICH COMPRISES CONTACTING ANALPHA-NITROKETONE WITH AN OXYGENATED POLAR APROTIC SOLVENT AT ATEMPERATURE OF FROM ABOUT 70*C. TO 200*C.
 2. A method according to claim1 wherein said temperature is from about 90* to 170*C.
 3. A methodaccording to claim 1 wherein the mole ratio of said nitroketone to saidsolvent is from about 1:3 to 1:100.
 4. A method according to claim 1wherein the mole ratio of said nitroketone to said solvent is from about1:10 to 1:50.
 5. A method according to claim 1 wherein said contactingis at a pressure of from atmospheric to 300 p.s.i.g.
 6. A methodaccording to claim 1 wherein said solvent is dimethylsulfoxide.
 7. Amethod according to claim 1 wherein said solvent is dimethylformamide.8. A method according to claim 1 wherein said solvent is1-methyl-2-pyrrolidinone.
 9. A method according to claim 1 wherein saidsolvent is acetone.
 10. A method according to claim 1 wherein saidsolvent is dimethylacetamide.
 11. A method according to claim 1 whereinsaid contacting is conducted in the presence of an inert liquid diluentboiling between about 80* and 200*C.
 12. A method according to claim 1wherein said alpha-nitroketone corresponds to the formula:
 13. A methodaccording to claim 1 wherein said nitroketone is 1-nitro-2-Propanone andwhere said alkylamide is acetamide.
 14. A method according to claim 1wherein said nitroketone is 1-nitro-2-hexadecanone and where saidalkylamide is pentadecanamide.
 15. A method according to claim 1 wherecarbon dioxide formed as a co-product is recovered.
 16. A method ofpreparing an alkylamide which comprises (1) nitrooxidizing a 1-olefin bycontacting with dinitrogen tetroxide and oxygen to form anitroalkylperoxy nitrate, (2) contacting said peroxy nitrate with adenitrating agent to form an alpha-nitroketone and (3) contacting saidnitroketone with an oxygenated polar aprotic solvent at a temperature offrom about 70*C. to 200*C.